For updating bank records like address change, name change etc , bank need documentary proof and KYC documents.
Generally names are changed by due process of legal and governmental formalities like witnessing and notarising the affidavi, publishing in newspaper, publishing in Official Gazette etc. Nowadays you may need to change the name in PAN card, Voter ID card and Aadhaar to be uniform.
As banks ask one or other documentary proof like Aadhaar, Voter ID card with photo etc you have to get these also corrected with the new changed name. After these you can approach your bank and ask for name change, complying all the stipulated KYC formalities.
However especially if you have availed some loan or overdraft, especially with guarantee from others, the banks may stipulate a few more formalities like freezing the exiting loan or asking to liquidate that loan or converting that loan liability into anew loan complying all formalities including concurrence of the guarantor.
It is better to meet the bank officials rather than writing a letter, as there may be some specifics which may be cleared only by interaction with the officials.
However for academic sake the I am giving a sample format for writing aletter to you bank for name change in your accounts, assumingthat you have all necessary documentary proof complying the legal/statutory formalities as described earlier:
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Place
Date
From(your name &address details)
To( The Bank Branch Head designation and bank branch address)
Ref/Subject: (Your account number(s) with that bank branch)
Request for name change in my bank records
Dear Sir, With reference to the above I request you to change my existing name( the existing name in the bank records) to my new name( new name as per gazette notification and documentary proof-all identical) and update your records accordingly .
I am enclosing the following documents for your perusal and records.
Kindly do the needful in this regard.
Thanking You
(signature )
(name)
enclosure details:
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However I suggest that you visit the bank with all your records like pass book, credit card, proof documents in original and copies etc and personally meet the bank officials. You may do the same after contacting them over phone and fixing a mutually convenient time.